Fishes of the Western North Atlantic 45 



Genus Petromyzon Linnaeus, 1758 

 Lampreys 



Petromyzon (in part) Linnaeus, Syst. Nat., 1758: 230; type species, P. mariiius Linnaeus. European seas. 

 Generic Synonyms: 



A. Adult. 



Bathyviyzon Gill, Proc. U.S. nat. Mus., 6, 1883: 254; type species, B. bairJii Gill. Continental slope off Cape 



Cod, Lat. 40° 02' N., Long. 68° 51' W., 547 fathoms.">= 

 Oceanomyzon Fowler, Proc. Acad. nat. Sci. Philad., 59, 1908: 461 ; type species, O. zvihoni Fowler. Atlantic 



Ocean. 



B. Larva. 



Ammocoetus (in part) Dumeril, Dissert. Poiss., 1812: 16; generic diagnosis, no species mentioned. 



Atnmocoetes (in part) Cuvier, Regnc .Anim., 2, 1817: 119; emended spelling ior Ammocoetus Blainville, 1 81 2; 

 type species, Petromyzon branchiaVts Linnaeus, 1758: 230 (larva of Lam.fetra fiuriatilis Linnaeus, 1758; 

 however, the larva of Petromyzon marinus is not distinguishable from it).°' 



Amm.ocaetes (in part) Beithold, in Latreille's Natur. Famil. Tierreich, 1827: 109; emended spelling for 

 Ammocoetes CM\-\e.T, 1817, and Ammocoetus BLiinville, 1812. 



Ammocites (in part) Beithold, in Latreille's Natur. Famil. Tierreich, 1827: 564 (index); evidently a mis- 

 spelling. 



Generic Characters. Two dorsal fins, the ist separated from 2nd by a definite inter- 

 space, the 2nd demarked from caudal by a deep notch, but continuous with it basally; 

 teeth renewed periodically by growth, combined with a periodic sloughing off of the outer- 

 most horny layer, those on oral disc, also called labial teeth, close together in regular 

 arrangement, the inner series much the largest, the outer series radiating outward in curved 

 rows: supraoral dental plate small, with 2 teeth; infraoral dental plate broad, with 7 to 9 

 conical teeth (see footnote 57, p. 47) ; tongue with 3 denticulated plates, the anterior 

 deeply indented anteriorly in the midline, its toothed margin biconcave; about 70 myo- 

 meres between rearmost gill opening and anus. 



Larva worm-like in appearance, toothless, the oral disc of adult represented in young 

 by a broad hood-like upper lip and very short lower lip; complexly branched papillae sur- 

 rounding mouth and present on midzone of upper lip ; eyes rudimentary and not visible ex- 

 ternally; fins without rays; dorsals not at all, or only faintly, demarked from each other 

 or from the caudal; muscular segmentation evident externally; gill sacs opening directly 

 into the pharynx internally; cartilaginous branchial basket rudimentary; pharynx with a 

 ventral ciliated pocket, a peripharyngeal ciliated groove anteriorly and a dorsal ciliated 

 tract ; "* gall bladder and bile duct present. 



52. This specimen, 275 mm. long, was made the basis of the new genus Bathymyzon because its supraoral and infra- 

 oral dental plates lacked distinct tubercles. But our own examination of the type specimen (U.S. nat. Mus., 

 No. 3331 1) has shown that it simply represents a case where the tubercles have been worn down prior to their 

 renewal, for a fresh set of very sharp tubercles is exposed when the outer layer of the suboral plate is lifted 

 free at one end. This appears to apply equally to the type specimen of Oceanomyzon Fowler, 1908. 



53. The parentage of the Amm.ocoete larva of Lamfetra fluviatilis was established by A. Miiller (Arch. Anat. 

 Physiol, wiss. Med., 1856: 323). 



54. For description of these, see Dohrn (Mitt. zool. Sta. Neapel, 6, 1886: 59) and Shipley (Quart. J. micr. Sci., 37, 

 1887:325). 



